A plasma is a collection of charged particles that may be used to remove material from or deposit material on a workpiece. Plasmas are used in the manufacture of integrated circuit (IC) devices, flat panel displays and other products. Plasmas may be used, for example, to etch (i.e., remove) material from or to sputter (i.e., deposit) material onto a workpiece in the form of, for example, a semiconductor substrate during IC fabrication.
A plasma may be formed by introducing a low pressure process gas into a plasma chamber and then applying a radio frequency (RF) power signal from a RF power source to the gas to ionize the gas particles. The RF source may be coupled to the plasma through a capacitance, through an inductance, or through both a capacitance and an inductance. When capacitive coupling is used, the plasma processing system may include one or more RF power sources, each of which operates at a selected frequency and each of which is electrically communicated to the process gas through an associated electrode.
A plasma chamber may include, for example, a first or chuck electrode that supports the workpiece within the chamber and a second electrode that together with the first electrode form a parallel plate capacitively coupled plasma (CCP) source. The chuck electrode (and therefore the workpiece) is appropriately electrically biased so that ions generated in the plasma chamber flow toward and strike the substrate for etching or deposition. To better control the processing of the workpiece, it would be advantageous to be able to determine the energy of the ions striking the workpiece.